1. Technical Field
The present invention relates to a detecting apparatus including a target section in which target elements to be detected are arrayed in the direction of movement of a moving body and a detecting section that detects the target elements with the movement of the moving body and outputs a waveform signal with an output level responsive to its detection sensitivity.
The invention further relates to recording units typified by facsimile machines and printers and, in particular, to a recording unit configured to transport recording media by a transport belt having a transport surface moving in the direction of transportation of the recording media.
2. Related Art
Recording units typified by facsimile machines and printers have a detector for sensing the amount and speed of the motion of a moving body, for example, a carriage equipped with a record head, a transport belt for transporting recording media, and a transport roller for transporting the recording media.
Examples of the detector include a non-contact type and a contact type. One example of the non-contact type is a detecting apparatus equipped with a linear scale or a rotary scale serving as a target section in which target elements, such as a light transmitting section and a light shielding section, are alternately arrayed and a detecting section that detects the light transmitting section and the light shielding section with the motion of the moving body and outputs a waveform signal. One example of the contact type is a detecting apparatus equipped with a magnetic recording layer in which magnetic poles, the south pole and the north pole, are alternately arrayed and a detecting section that detects changes in the magnetic poles of the magnetic recording layer with the motion of the moving body and outputs a waveform signal.
Ink jet printers that record on a recording medium by ejecting ink sometimes become unable to detect the target elements because of adhesion of floating mist ink to the target elements. Recording units other than the ink jet type sometimes become unable to detect the target elements because of adhesion of paper powder generated in a paper transport path, abrasion powder generated from a sliding portion, or extraneous dust to the target element.
To solve the above problems, there are various arts. JP-A-2003-145877 describes a serial printer having a detector for detecting the abnormality of an encoder signal, and when an abnormal output of the encoder signal is detected, a motor for driving the carriage is stopped to thereby prevent the runaway of the carriage.
JP-A-2001-121721 discloses a recording unit in which a linear encoder sensor is cleaned when the contamination of the linear encoder sensor is detected. JP-A-2003-175650 discloses an image forming apparatus configured to compensate the dropout or changes of a carriage position signal to execute normal print control.
JP-A-2006-213042 describes an image forming apparatus in which when the contamination of an encoder is detected, abnormality information is sent to a display device or the like of the operation panel to inform the user of the generation of the contamination of the encoder.
JP-A-2002-13950 describes an encoder that determines the midpoint of the slits of an encoder scale plate by determining the midpoint of the distribution of the electric signals output from a photo detector using two thresholds for the output level of the electric signals to find the mean value of the midpoints determined using the individual thresholds as the midpoint of the slits.
If the distribution of the electric signals is distorted because of the contamination or foreign matter, such as dust, adhered to the encoder scale plate, so that the difference between the midpoints of the distribution of the electric signals determined using the two thresholds becomes larger than a predetermined value, the encoder does not use the midpoints determined using the individual thresholds to determine the slit midpoint position, thereby minimizing errors as soon as possible.
Although there are various arts for solving the problems due to the contamination of target elements, the following technical problems still remain. In the serial printer described in JP-A-2003-145877, if an abnormal output of the encoder signal is detected, the operation of the motor for driving the carriage is stopped, so that the printing operation is stopped halfway, thus resulting in the waste of recording paper. Such a technical problem and means for solving this problem are not described also in JP-A-2001-121721, JP-A-2003-175650, and JP-A-2002-13950.
The image forming apparatus described in JP-A-2006-213042 is configured not to disable the use of the apparatus soon if the contamination is slight by determining that the encoder is contaminated only when two or more times of abnormal speed occur at the same portion of the encoder scale.
However, if two or more times of abnormal speed occur at the same portion of the encoder scale, printing is stopped, and the origin point of the carriage is adjusted, and then the remaining printing is executed. This may cause a waste of paper at the stop of the printing. If printing on paper is stopped, and the origin point of the carriage is adjusted and then the printing is started again, the recording quality may be extremely deteriorated.